Normally, the actuator device comprises an electric gearmotor, which is generally mounted outside the support body on a peripheral zone of the lower portion with an output shaft thereof parallel to the longitudinal axis, and a transmission device, which is arranged inside the support body and normally consists of a mechanical geared transmission comprising a pinion keyed on the output shaft of the gearmotor and a toothed crown meshing with the pinion and rigidly connected to the upper portion.
The known antenna base described above has some drawbacks related, on one hand, to the presence of the gearmotor, which, being mounted outside the support body and in offset position with respect to the longitudinal axis, determines a considerable asymmetry in the total volume of the antenna base, with consequent problems of clearance and balancing of weights, and, on the other hand, to the presence of the geared transmission, which, in addition to having a large size and heavy weight, is subject to considerable wear, above all in critical working environments with the presence of dust, salt mist etc., and therefore requires frequent preventive and corrective maintenance interventions.
Furthermore, in order to guarantee the correct operation of the mechanical transmission, the support body must necessarily be provided with a gear lubrication system, normally an oil bath lubrication system, which considerably complicates the support body structure and implies the use of large amounts of “polluting” materials, such as lubricating oils.
Finally, a further drawback is constituted by the running noise, mainly deriving from the mechanical transmission.
The drawbacks described above are particularly critical when the known antenna described above is used in mobile land or maritime systems, in which light weight, compactness and limited need for maintenance interventions are particularly desirable requirements.
GB2257301, GB1295928, U.S. Pat. Nos. 3,486,053 and 2,901,208 suggest the use of an induction motor comprising a fixed part, the stator, connected to the fixed portion of the support body of the antenna and a mobile part, the rotor, connected to the antenna. These systems, however, suffer from the drawback of presenting relatively complex structures and are difficult to assemble, disassemble and maintain.